llvm-project

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//===--- examples/Fibonacci/fibonacci.cpp - An example use of the JIT -----===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// This small program provides an example of how to build quickly a small module
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// with function Fibonacci and execute it with the JIT.
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//
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// The goal of this snippet is to create in the memory the LLVM module
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// consisting of one function as follow:
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//
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//   int fib(int x) {
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//     if(x<=2) return 1;
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//     return fib(x-1)+fib(x-2);
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//   }
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//
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// Once we have this, we compile the module via JIT, then execute the `fib'
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// function and return result to a driver, i.e. to a "host program".
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//
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//===----------------------------------------------------------------------===//
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#include "llvm/ADT/APInt.h"
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#include "llvm/IR/Verifier.h"
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#include "llvm/ExecutionEngine/ExecutionEngine.h"
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#include "llvm/ExecutionEngine/GenericValue.h"
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#include "llvm/ExecutionEngine/MCJIT.h"
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#include "llvm/IR/Argument.h"
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#include "llvm/IR/BasicBlock.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/DerivedTypes.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/InstrTypes.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/LLVMContext.h"
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#include "llvm/IR/Module.h"
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#include "llvm/IR/Type.h"
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#include "llvm/Support/Casting.h"
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#include "llvm/Support/TargetSelect.h"
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#include "llvm/Support/raw_ostream.h"
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#include <algorithm>
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#include <cstdlib>
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#include <memory>
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#include <string>
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#include <vector>
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using namespace llvm;
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static Function *CreateFibFunction(Module *M, LLVMContext &Context) {
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  // Create the fib function and insert it into module M. This function is said
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  // to return an int and take an int parameter.
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  FunctionType *FibFTy = FunctionType::get(Type::getInt32Ty(Context),
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                                           {Type::getInt32Ty(Context)}, false);
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  Function *FibF =
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      Function::Create(FibFTy, Function::ExternalLinkage, "fib", M);
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  // Add a basic block to the function.
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  BasicBlock *BB = BasicBlock::Create(Context, "EntryBlock", FibF);
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  // Get pointers to the constants.
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  Value *One = ConstantInt::get(Type::getInt32Ty(Context), 1);
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  Value *Two = ConstantInt::get(Type::getInt32Ty(Context), 2);
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  // Get pointer to the integer argument of the add1 function...
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  Argument *ArgX = &*FibF->arg_begin(); // Get the arg.
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  ArgX->setName("AnArg");            // Give it a nice symbolic name for fun.
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  // Create the true_block.
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  BasicBlock *RetBB = BasicBlock::Create(Context, "return", FibF);
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  // Create an exit block.
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  BasicBlock* RecurseBB = BasicBlock::Create(Context, "recurse", FibF);
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  // Create the "if (arg <= 2) goto exitbb"
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  Value *CondInst = new ICmpInst(BB, ICmpInst::ICMP_SLE, ArgX, Two, "cond");
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  BranchInst::Create(RetBB, RecurseBB, CondInst, BB);
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  // Create: ret int 1
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  ReturnInst::Create(Context, One, RetBB);
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  // create fib(x-1)
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  Value *Sub = BinaryOperator::CreateSub(ArgX, One, "arg", RecurseBB);
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  CallInst *CallFibX1 = CallInst::Create(FibF, Sub, "fibx1", RecurseBB);
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  CallFibX1->setTailCall();
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  // create fib(x-2)
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  Sub = BinaryOperator::CreateSub(ArgX, Two, "arg", RecurseBB);
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  CallInst *CallFibX2 = CallInst::Create(FibF, Sub, "fibx2", RecurseBB);
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  CallFibX2->setTailCall();
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  // fib(x-1)+fib(x-2)
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  Value *Sum = BinaryOperator::CreateAdd(CallFibX1, CallFibX2,
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                                         "addresult", RecurseBB);
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  // Create the return instruction and add it to the basic block
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  ReturnInst::Create(Context, Sum, RecurseBB);
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  return FibF;
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}
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int main(int argc, char **argv) {
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  int n = argc > 1 ? atol(argv[1]) : 24;
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  InitializeNativeTarget();
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  InitializeNativeTargetAsmPrinter();
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  LLVMContext Context;
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  // Create some module to put our function into it.
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  std::unique_ptr<Module> Owner(new Module("test", Context));
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  Module *M = Owner.get();
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  // We are about to create the "fib" function:
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  Function *FibF = CreateFibFunction(M, Context);
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  // Now we going to create JIT
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  std::string errStr;
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  ExecutionEngine *EE =
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    EngineBuilder(std::move(Owner))
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    .setErrorStr(&errStr)
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    .create();
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  if (!EE) {
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    errs() << argv[0] << ": Failed to construct ExecutionEngine: " << errStr
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           << "\n";
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    return 1;
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  }
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  errs() << "verifying... ";
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  if (verifyModule(*M)) {
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    errs() << argv[0] << ": Error constructing function!\n";
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    return 1;
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  }
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  errs() << "OK\n";
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  errs() << "We just constructed this LLVM module:\n\n---------\n" << *M;
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  errs() << "---------\nstarting fibonacci(" << n << ") with JIT...\n";
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  // Call the Fibonacci function with argument n:
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  std::vector<GenericValue> Args(1);
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  Args[0].IntVal = APInt(32, n);
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  GenericValue GV = EE->runFunction(FibF, Args);
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  // import result of execution
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  outs() << "Result: " << GV.IntVal << "\n";
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  return 0;
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}
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